Add a spell check workflow

[jishnub]

Re-targets the content of #692 onto master.

#692 was opened against jishnub/typos while it was still the base of the stack. jishnub/typos was squash-merged into master as #691 before #692 landed, so #692 ended up merged into a branch that is not an ancestor of master — the typo fixes made it in, but the workflow that keeps them from coming back did not. master has no typos.yml and no _typos.toml today.

This is the same two files, rebased onto current master. Nothing else changed.

_typos.toml allowlists what the default dictionary flags in this package, all identifiers or abbreviations rather than prose:

Entry	Why
OT	order type parameter of the calculus operators
Wrapp	WrappOp, generated by @calculus_operator
opf	built by Symbol(:op, f) in the operator definitions
ND	TensorSpaceND
BA, iy, kend, shft	local variables
Comput	SIAM J. Sci. Comput. in a citation
Overrideable	spelling variant in a section header
SPECIALOPS	the name referred to by a TODO comment

Verified with typos v1.49.0 against this branch: clean, and still catches new mistakes (planting recieve/seperate in a comment fails the check).

🤖 Generated with Claude Code